Fiber optic cables and their associated electronics are widely used for providing telephony, data and other related communications services. A fiber optic communication system typically offers immunity to electrical noise, a relatively large information carrying bandwidth, and low signal losses. The fiber optic cables are readily installed in existing city duct lines, on overhead pole lines, or direct buried in the earth to thereby form cable networks including a plurality of users.
One particularly advantageous use of fiber optic technology is for a ring or loop in a metropolitan or city setting. Unfortunately, one potential disadvantage of an optical fiber cable, as compared to radio, for example, is that an inadvertent cable cut will disrupt communication over the cut cable. Accordingly, it is common to provide a cable network for a metropolitan area, for example, in the form of a ring, and to provide redundant electronics coupled to the cable ring.
The cable ring and electronics provide two possible paths of communication. If the cable is cut in the first path, then communications is directed in the opposite direction over the second path of the cable ring. The cut fiber cable may then be repaired and full service restored.
Such a fiber optic network or system is commonly used in a downtown or metropolitan environment where individual fibers originate at a telephone company or service provider central office and are dropped at various office buildings or other large communications users along the ring. Typically the cable of the ring has a relatively large fiber count, such as, for example, from 96 to 144 fibers. A typical user may only use two fibers from the ring--one for transmit and one for receive. In addition, the electronics can typically switch directions, such as in the event of a cable cut.
A user is typically connected to the ring at a drop point using two separate splice closures. The main closure is connected to adjacent legs of the main or ring cable. A majority of the individual optical fibers may be spliced directly between the two adjacent legs. Alternately, a majority of the non-dropped fibers may be directly passed through without splicing.
In addition, a pair of relatively low count fiber optic drop cables are spliced at their first ends to predetermined ones of the fibers from the ring cable in the main closure. The low fiber count drop cables may be about 60 feet in length and connect to a drop closure. Drop fibers are connected to the ends of the two drop cables, and fibers which are not dropped are spliced together in the drop closure. The dropped fibers are connected to electronic equipment, and some fibers may be set aside as spares for future use. The main splice closure, the drop cables, and the drop splice closure are typically grouped together in a manhole or vault and consume a relatively large amount of space. In addition to the cost and space required, the large number of splices and the lack of flexibility to add additional drops are significant disadvantages of this conventional approach.
Of course the prior art discloses many different versions of splice closures. One typical configuration includes pivoting generally elongate and rectangular splice organizer trays positioned to extend longitudinally within a splice enclosure. For example, U.S. Pat. No. 5,515,472 to Mullaney et al., and assigned to the assignee of the present invention, discloses such a splice closure. The closure also includes a bottom slack storage tray portion for storing buffer tubes.
U.S. Pat. No. 5,155,794 to Nolf et al., and also assigned to the assignee of the present invention; U.S. Pat. No. 5,185,845 to Jones; U.S. Pat. No. 4,927,227 to Bensel, III et al.; U.S. Pat. No. 5,553,186 to Allen; U.S. Pat. No. 5,590,234 to Pulido; and U.S. Pat. No. 5,617,501 to Miller et al. also each disclose generally rectangular, pivotally connected splice trays within an overall housing. U.S. Pat. No. 5,619,608 to Foss et al. discloses a plurality of elliptical trays arranged in a stack at a common angle to an axis of the stack. U.S. Pat. No. 5,717,811 to Macken, also assigned to the present assignee, discloses a series of splice organizer trays having rounded outer ends and which are arranged in a stack at an inclined angle. This patent is directed to an organizer that is able to handle both live fiber, and dark fiber--a dark fiber end being a free end of the fiber that is being stored for possible future use. The patent further discloses that a module of trays may be preinstalled with fibers.
Unfortunately, despite the continued improvements and developments in the area of splice closures, at present the multiple closure and drop cable configuration is most commonly used for the drop locations along a ring network. As already mentioned above, the use of main and drop splices consumes considerable space, is labor intensive, and may not be sufficiently flexible for the subscriber or end user should additions or changes be needed.